Portion of a display screen showing a user interface



The FIGURE is a front view showing the new design.

The broken line showing of various regions in the FIGURE and the unshaded areas there within form no part of the claimed design. The outer rectangle shown in broken line is for the purpose of showing a portion of a display screen and forms no part of the claimed design. 

The ornamental design for a portion of a display screen showing a user interface, as shown and described. 